Recent therapeutic attempts include a variety of cytokines, hematopoietic growth factors, or specific ligands for the modulation of immune responses and hematopoiesis for the treatment of various clinical conditions or as adjuvant to immunization protocols. A significant number of such applications are studied using various nonhuman primate models, yet while most human factors appear biologically active in nonhuman primates, data shows that injection of human recombinant cytokines most often does not allow repeated or long-term treatment due to rapid development of an immune response towards these "foreign" molecules, resulting in inactivation and clearance of these cytokines. Furthermore the immune response of primate cells to the stimulation by certain human cytokines has been found to be markedly lower than the response of equivalent cells from human origins. These studies bear the potential to rapidly translate into therapeutic applications for the treatment of human diseases.